Conventionally, an adaptive array antenna apparatus has an array antenna including a plurality of antenna elements. Based on a signal received by each antenna element and a known reference signal, array weights (complex numbers) for the antenna elements are adaptively computed, and the received signals of the antenna elements are subjected to weighting synthesis using the weight array of the complex numbers, thereby forming directivity of the array antenna.
For example, in the conventional technique disclosed in Patent Document 1, in order to install an adaptive array antenna to an existing wireless apparatus which does not employ an adaptive array antenna, the received signal having a radio frequency (RF)) of each antenna element is converted into a lower frequency (e.g., baseband frequency), and then subjected to weighting for the amplitude and phase thereof. After that the received signals of the antenna elements are synthesized, and the frequency of the synthesized signal is converted to a higher RF. The RF signal is then supplied to the existing wireless apparatus.
On the other hand, when in a known technique for synthesizing the received signals of the antenna elements into one signal, the received signal of each antenna element is separated into an in-phase element (I channel) and a quadrature element (Q channel), and the total sum of the signals of the antenna elements is independently computed for each of the T and Q channels (see, for example, FIG. 1 of Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 200149053.
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2005-318318.
However, in the conventional technique disclosed in Patent Document 1, the received signal of each antenna element is converted to have a frequency (e.g., baseband) lower than the input frequency (e.g., RF) of the existing wireless apparatus, and then weighting synthesis of the signals is performed. Therefore, after the synthesis, the frequency of the relevant received signal should be again raised to the input frequency of the existing wireless apparatus. In this case, a frequency upconverter (e.g., a local signal generator or a mixer) is required. In addition, as a frequency up-converter such as a mixer performs non-linear processing, a signal distortion may occur during the processing.
Additionally, in the conventional technique disclosed in Patent Document 2, when synthesizing the received signals of the antenna elements, I and Q channels each require an adder.
As described above, in the conventional techniques, the system store may be complex, the manufacturing cost may increase, and the signal reception quality may degrade.